Challenges in the Diagnosis of Eosinophilic Colitis: Insights from Cases Initially Diagnosed as Inflammatory Bowel Disease.

Introduction: Eosinophilic colitis (EoC) is an immune-mediated disorder characterized by chronic colitis with significant eosinophilic infiltration. Diagnosing EoC is sometimes challenging due to more common disorders associated with colonic eosinophilia like inflammatory bowel disease (IBD). This study aimed to examine the prevalence and clinical features of patients who were initially diagnosed with IBD and later found to have EoC (IBD-EoC) and to identify the clinical factors facilitating a definitive EoC diagnosis. Methods: Medical records of patients with eosinophilic gastrointestinal diseases (EGIDs) were retrospectively reviewed and subsequently analyzed for the cases of IBD-EoC. Clinical characteristics were compared between patients with IBD-EoC and those initially diagnosed with EoC (definitive EoC). Results: Among 42 patients with EGIDs, 4 were diagnosed with EoC. Two of them were definitive EoC, while the remaining 2 were initially diagnosed with IBD (IBD-EoC), representing 0.64% of patients with IBD. Unlike in patients with definitive EoC, the endoscopic findings atypically suggestive of IBD and the possibility of EoC were not communicated between the endoscopists and the pathologists in patients with IBD-EoC. The absence of mucosal eosinophil count in the initial histologic report further delayed the diagnosis of EoC. Treatment failure with 5-ASA prompted the reassessment of endoscopic and histologic findings, leading to the revised diagnosis of EoC. The presence of peripheral blood eosinophilia facilitated the initial diagnosis with EoC in patients with definitive EoC. Conclusion: Proactive communication between endoscopists and pathologists is crucial for diagnosing EoC.